diff mbox series

[RFC] selinux: deprecate disabling SELinux and runtime

Message ID 157678334821.158235.2125894638773393579.stgit@chester (mailing list archive)
State Superseded
Headers show
Series [RFC] selinux: deprecate disabling SELinux and runtime | expand

Commit Message

Paul Moore Dec. 19, 2019, 7:22 p.m. UTC
Deprecate the CONFIG_SECURITY_SELINUX_DISABLE functionality.  The
code was originally developed to make it easier for Linux
distributions to support architectures where adding parameters to the
kernel command line was difficult.  Unfortunately, supporting runtime
disable meant we had to make some security trade-offs when it came to
the LSM hooks, as documented in the Kconfig help text:

  NOTE: selecting this option will disable the '__ro_after_init'
  kernel hardening feature for security hooks.   Please consider
  using the selinux=0 boot parameter instead of enabling this
  option.

Fortunately it looks as if that the original motivation for the
runtime disable functionality is gone, and Fedora/RHEL appears to be
the only major distribution enabling this capability at build time
so we are now taking steps to remove it entirely from the kernel.
The first step is to mark the functionality as deprecated and print
an error when it is used (what this patch is doing).  As Fedora/RHEL
makes progress in transitioning the distribution away from runtime
disable, we will introduce follow-up patches over several kernel
releases which will block for increasing periods of time when the
runtime disable is used.  Finally we will remove the option entirely
once we believe all users have moved to the kernel cmdline approach.

Signed-off-by: Paul Moore <paul@paul-moore.com>
---
 security/selinux/Kconfig     |    3 +++
 security/selinux/selinuxfs.c |    6 ++++++
 2 files changed, 9 insertions(+)

Comments

Casey Schaufler Dec. 19, 2019, 11:40 p.m. UTC | #1
On 12/19/2019 11:22 AM, Paul Moore wrote:
> Deprecate the CONFIG_SECURITY_SELINUX_DISABLE functionality.  The
> code was originally developed to make it easier for Linux
> distributions to support architectures where adding parameters to the
> kernel command line was difficult.  Unfortunately, supporting runtime
> disable meant we had to make some security trade-offs when it came to
> the LSM hooks, as documented in the Kconfig help text:
>
>   NOTE: selecting this option will disable the '__ro_after_init'
>   kernel hardening feature for security hooks.   Please consider
>   using the selinux=0 boot parameter instead of enabling this
>   option.
>
> Fortunately it looks as if that the original motivation for the
> runtime disable functionality is gone, and Fedora/RHEL appears to be
> the only major distribution enabling this capability at build time
> so we are now taking steps to remove it entirely from the kernel.
> The first step is to mark the functionality as deprecated and print
> an error when it is used (what this patch is doing).  As Fedora/RHEL
> makes progress in transitioning the distribution away from runtime
> disable, we will introduce follow-up patches over several kernel
> releases which will block for increasing periods of time when the
> runtime disable is used.  Finally we will remove the option entirely
> once we believe all users have moved to the kernel cmdline approach.
>
> Signed-off-by: Paul Moore <paul@paul-moore.com>

Acked-by: Casey Schaufler <casey@schaufler-ca.com>

> ---
>  security/selinux/Kconfig     |    3 +++
>  security/selinux/selinuxfs.c |    6 ++++++
>  2 files changed, 9 insertions(+)
>
> diff --git a/security/selinux/Kconfig b/security/selinux/Kconfig
> index 996d35d950f7..580ac24c7aa1 100644
> --- a/security/selinux/Kconfig
> +++ b/security/selinux/Kconfig
> @@ -42,6 +42,9 @@ config SECURITY_SELINUX_DISABLE
>  	  using the selinux=0 boot parameter instead of enabling this
>  	  option.
>  
> +	  WARNING: this option is deprecated and will be removed in a future
> +	  kernel release.
> +
>  	  If you are unsure how to answer this question, answer N.
>  
>  config SECURITY_SELINUX_DEVELOP
> diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
> index 278417e67b4c..adbe2dd35202 100644
> --- a/security/selinux/selinuxfs.c
> +++ b/security/selinux/selinuxfs.c
> @@ -281,6 +281,12 @@ static ssize_t sel_write_disable(struct file *file, const char __user *buf,
>  	int new_value;
>  	int enforcing;
>  
> +	/* NOTE: we are now officially considering runtime disable as
> +	 *       deprecated, and using it will become increasingly painful
> +	 *       (e.g. sleeping/blocking) as we progress through future
> +	 *       kernel releases until eventually it is removed */
> +	pr_err("SELinux:  Runtime disable is deprecated, use selinux=0 on the kernel cmdline.\n");
> +
>  	if (count >= PAGE_SIZE)
>  		return -ENOMEM;
>  
>
>
Ondrej Mosnacek Jan. 2, 2020, 9:23 a.m. UTC | #2
On Thu, Dec 19, 2019 at 8:22 PM Paul Moore <paul@paul-moore.com> wrote:
> Deprecate the CONFIG_SECURITY_SELINUX_DISABLE functionality.  The
> code was originally developed to make it easier for Linux
> distributions to support architectures where adding parameters to the
> kernel command line was difficult.  Unfortunately, supporting runtime
> disable meant we had to make some security trade-offs when it came to
> the LSM hooks, as documented in the Kconfig help text:
>
>   NOTE: selecting this option will disable the '__ro_after_init'
>   kernel hardening feature for security hooks.   Please consider
>   using the selinux=0 boot parameter instead of enabling this
>   option.
>
> Fortunately it looks as if that the original motivation for the
> runtime disable functionality is gone, and Fedora/RHEL appears to be
> the only major distribution enabling this capability at build time
> so we are now taking steps to remove it entirely from the kernel.
> The first step is to mark the functionality as deprecated and print
> an error when it is used (what this patch is doing).  As Fedora/RHEL
> makes progress in transitioning the distribution away from runtime
> disable, we will introduce follow-up patches over several kernel
> releases which will block for increasing periods of time when the
> runtime disable is used.  Finally we will remove the option entirely
> once we believe all users have moved to the kernel cmdline approach.
>
> Signed-off-by: Paul Moore <paul@paul-moore.com>

Looks reasonable, informal ACK from me.

> ---
>  security/selinux/Kconfig     |    3 +++
>  security/selinux/selinuxfs.c |    6 ++++++
>  2 files changed, 9 insertions(+)
>
> diff --git a/security/selinux/Kconfig b/security/selinux/Kconfig
> index 996d35d950f7..580ac24c7aa1 100644
> --- a/security/selinux/Kconfig
> +++ b/security/selinux/Kconfig
> @@ -42,6 +42,9 @@ config SECURITY_SELINUX_DISABLE
>           using the selinux=0 boot parameter instead of enabling this
>           option.
>
> +         WARNING: this option is deprecated and will be removed in a future
> +         kernel release.
> +
>           If you are unsure how to answer this question, answer N.
>
>  config SECURITY_SELINUX_DEVELOP
> diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
> index 278417e67b4c..adbe2dd35202 100644
> --- a/security/selinux/selinuxfs.c
> +++ b/security/selinux/selinuxfs.c
> @@ -281,6 +281,12 @@ static ssize_t sel_write_disable(struct file *file, const char __user *buf,
>         int new_value;
>         int enforcing;
>
> +       /* NOTE: we are now officially considering runtime disable as
> +        *       deprecated, and using it will become increasingly painful
> +        *       (e.g. sleeping/blocking) as we progress through future
> +        *       kernel releases until eventually it is removed */
> +       pr_err("SELinux:  Runtime disable is deprecated, use selinux=0 on the kernel cmdline.\n");
> +
>         if (count >= PAGE_SIZE)
>                 return -ENOMEM;
>
>
Paul Moore Jan. 2, 2020, 9:38 p.m. UTC | #3
On Thu, Jan 2, 2020 at 4:24 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> On Thu, Dec 19, 2019 at 8:22 PM Paul Moore <paul@paul-moore.com> wrote:
> > Deprecate the CONFIG_SECURITY_SELINUX_DISABLE functionality.  The
> > code was originally developed to make it easier for Linux
> > distributions to support architectures where adding parameters to the
> > kernel command line was difficult.  Unfortunately, supporting runtime
> > disable meant we had to make some security trade-offs when it came to
> > the LSM hooks, as documented in the Kconfig help text:
> >
> >   NOTE: selecting this option will disable the '__ro_after_init'
> >   kernel hardening feature for security hooks.   Please consider
> >   using the selinux=0 boot parameter instead of enabling this
> >   option.
> >
> > Fortunately it looks as if that the original motivation for the
> > runtime disable functionality is gone, and Fedora/RHEL appears to be
> > the only major distribution enabling this capability at build time
> > so we are now taking steps to remove it entirely from the kernel.
> > The first step is to mark the functionality as deprecated and print
> > an error when it is used (what this patch is doing).  As Fedora/RHEL
> > makes progress in transitioning the distribution away from runtime
> > disable, we will introduce follow-up patches over several kernel
> > releases which will block for increasing periods of time when the
> > runtime disable is used.  Finally we will remove the option entirely
> > once we believe all users have moved to the kernel cmdline approach.
> >
> > Signed-off-by: Paul Moore <paul@paul-moore.com>
>
> Looks reasonable, informal ACK from me.

Thanks.  You want to make that a formal ACK? ;)
Ondrej Mosnacek Jan. 3, 2020, 9:32 a.m. UTC | #4
On Thu, Jan 2, 2020 at 10:38 PM Paul Moore <paul@paul-moore.com> wrote:
>
> On Thu, Jan 2, 2020 at 4:24 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> > On Thu, Dec 19, 2019 at 8:22 PM Paul Moore <paul@paul-moore.com> wrote:
> > > Deprecate the CONFIG_SECURITY_SELINUX_DISABLE functionality.  The
> > > code was originally developed to make it easier for Linux
> > > distributions to support architectures where adding parameters to the
> > > kernel command line was difficult.  Unfortunately, supporting runtime
> > > disable meant we had to make some security trade-offs when it came to
> > > the LSM hooks, as documented in the Kconfig help text:
> > >
> > >   NOTE: selecting this option will disable the '__ro_after_init'
> > >   kernel hardening feature for security hooks.   Please consider
> > >   using the selinux=0 boot parameter instead of enabling this
> > >   option.
> > >
> > > Fortunately it looks as if that the original motivation for the
> > > runtime disable functionality is gone, and Fedora/RHEL appears to be
> > > the only major distribution enabling this capability at build time
> > > so we are now taking steps to remove it entirely from the kernel.
> > > The first step is to mark the functionality as deprecated and print
> > > an error when it is used (what this patch is doing).  As Fedora/RHEL
> > > makes progress in transitioning the distribution away from runtime
> > > disable, we will introduce follow-up patches over several kernel
> > > releases which will block for increasing periods of time when the
> > > runtime disable is used.  Finally we will remove the option entirely
> > > once we believe all users have moved to the kernel cmdline approach.
> > >
> > > Signed-off-by: Paul Moore <paul@paul-moore.com>
> >
> > Looks reasonable, informal ACK from me.
>
> Thanks.  You want to make that a formal ACK? ;)

Sure, if you find it useful :)

Acked-by: Ondrej Mosnacek <omosnace@redhat.com>
Paul Moore Jan. 3, 2020, 3:55 p.m. UTC | #5
On Fri, Jan 3, 2020 at 4:32 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> On Thu, Jan 2, 2020 at 10:38 PM Paul Moore <paul@paul-moore.com> wrote:
> > On Thu, Jan 2, 2020 at 4:24 AM Ondrej Mosnacek <omosnace@redhat.com> wrote:
> > > On Thu, Dec 19, 2019 at 8:22 PM Paul Moore <paul@paul-moore.com> wrote:
> > > > Deprecate the CONFIG_SECURITY_SELINUX_DISABLE functionality ...

...

> > > Looks reasonable, informal ACK from me.
> >
> > Thanks.  You want to make that a formal ACK? ;)
>
> Sure, if you find it useful :)
>
> Acked-by: Ondrej Mosnacek <omosnace@redhat.com>

Yes, it is useful, thank you.

For this patch your ACK is particularly significant because you are
representing RH here (I'm assuming you are still the RH SELinux kernel
person) and we are deprecating a feature used by Fedora.  In my
opinion it would be a mistake to merge a deprecation patch without the
ACKs of those who rely on the feature targeted for removal (although
in some cases it may need to be done regardless).

I also really dislike merging my own patches without at least one
other Acked-by/Reviewed-by tag for the simple reason that I believe
every patch should have at least two people (author and at least one
reviewer) who agree that the patch is reasonable.  Of course there are
exceptions for trivial and critical fixes, e.g. 15b590a81fcd
("selinux: ensure the policy has been loaded before reading the sidtab
stats"), but I like to keep those as the exception rather than the
rule.  Just because someone is listed in the MAINTAINERS file
shouldn't mean they are exempt from the normal review process.

Generally speaking, one of the more useful things one can do from an
upstream perspective is to review and test patches that are submitted
to the list.  We are a community driven project after all, and the
community aspect shouldn't be limited to just the development of
patches ;)
Stephen Smalley Jan. 6, 2020, 9:26 p.m. UTC | #6
On 12/19/19 2:22 PM, Paul Moore wrote:
> Deprecate the CONFIG_SECURITY_SELINUX_DISABLE functionality.  The
> code was originally developed to make it easier for Linux
> distributions to support architectures where adding parameters to the
> kernel command line was difficult.  Unfortunately, supporting runtime
> disable meant we had to make some security trade-offs when it came to
> the LSM hooks, as documented in the Kconfig help text:
> 
>    NOTE: selecting this option will disable the '__ro_after_init'
>    kernel hardening feature for security hooks.   Please consider
>    using the selinux=0 boot parameter instead of enabling this
>    option.
> 
> Fortunately it looks as if that the original motivation for the
> runtime disable functionality is gone, and Fedora/RHEL appears to be
> the only major distribution enabling this capability at build time
> so we are now taking steps to remove it entirely from the kernel.
> The first step is to mark the functionality as deprecated and print
> an error when it is used (what this patch is doing).  As Fedora/RHEL
> makes progress in transitioning the distribution away from runtime
> disable, we will introduce follow-up patches over several kernel
> releases which will block for increasing periods of time when the
> runtime disable is used.  Finally we will remove the option entirely
> once we believe all users have moved to the kernel cmdline approach.
> 
> Signed-off-by: Paul Moore <paul@paul-moore.com>
> ---
>   security/selinux/Kconfig     |    3 +++
>   security/selinux/selinuxfs.c |    6 ++++++
>   2 files changed, 9 insertions(+)
> 
> diff --git a/security/selinux/Kconfig b/security/selinux/Kconfig
> index 996d35d950f7..580ac24c7aa1 100644
> --- a/security/selinux/Kconfig
> +++ b/security/selinux/Kconfig
> @@ -42,6 +42,9 @@ config SECURITY_SELINUX_DISABLE
>   	  using the selinux=0 boot parameter instead of enabling this
>   	  option.
>   
> +	  WARNING: this option is deprecated and will be removed in a future
> +	  kernel release.
> +
>   	  If you are unsure how to answer this question, answer N.
>   
>   config SECURITY_SELINUX_DEVELOP
> diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
> index 278417e67b4c..adbe2dd35202 100644
> --- a/security/selinux/selinuxfs.c
> +++ b/security/selinux/selinuxfs.c
> @@ -281,6 +281,12 @@ static ssize_t sel_write_disable(struct file *file, const char __user *buf,
>   	int new_value;
>   	int enforcing;
>   
> +	/* NOTE: we are now officially considering runtime disable as
> +	 *       deprecated, and using it will become increasingly painful
> +	 *       (e.g. sleeping/blocking) as we progress through future
> +	 *       kernel releases until eventually it is removed */
> +	pr_err("SELinux:  Runtime disable is deprecated, use selinux=0 on the kernel cmdline.\n");

Looking for examples of similar deprecations in the kernel, I notice 
that they often use pr_warn_once() or WARN_ONCE() to avoid spamming the 
kernel logs excessively.  They also often include the current process 
name to identify the offending process.  In this case, it probably 
matters little since this is only done (legitimately) by the init 
process and only once, so up to you whether you bother amending it. 
Also for some interfaces, they appear to document the intent to remove 
it in a file under Documentation/ABI/obsolete/ and then later move that 
to removed/ when fully removed. Regardless,

Acked-by: Stephen Smalley <sds@tycho.nsa.gov>

> +
>   	if (count >= PAGE_SIZE)
>   		return -ENOMEM;
>   
>
Paul Moore Jan. 7, 2020, 3:29 a.m. UTC | #7
On Mon, Jan 6, 2020 at 4:25 PM Stephen Smalley <sds@tycho.nsa.gov> wrote:
> On 12/19/19 2:22 PM, Paul Moore wrote:
> > Deprecate the CONFIG_SECURITY_SELINUX_DISABLE functionality.  The
> > code was originally developed to make it easier for Linux
> > distributions to support architectures where adding parameters to the
> > kernel command line was difficult.  Unfortunately, supporting runtime
> > disable meant we had to make some security trade-offs when it came to
> > the LSM hooks, as documented in the Kconfig help text:
> >
> >    NOTE: selecting this option will disable the '__ro_after_init'
> >    kernel hardening feature for security hooks.   Please consider
> >    using the selinux=0 boot parameter instead of enabling this
> >    option.
> >
> > Fortunately it looks as if that the original motivation for the
> > runtime disable functionality is gone, and Fedora/RHEL appears to be
> > the only major distribution enabling this capability at build time
> > so we are now taking steps to remove it entirely from the kernel.
> > The first step is to mark the functionality as deprecated and print
> > an error when it is used (what this patch is doing).  As Fedora/RHEL
> > makes progress in transitioning the distribution away from runtime
> > disable, we will introduce follow-up patches over several kernel
> > releases which will block for increasing periods of time when the
> > runtime disable is used.  Finally we will remove the option entirely
> > once we believe all users have moved to the kernel cmdline approach.
> >
> > Signed-off-by: Paul Moore <paul@paul-moore.com>
> > ---
> >   security/selinux/Kconfig     |    3 +++
> >   security/selinux/selinuxfs.c |    6 ++++++
> >   2 files changed, 9 insertions(+)
> >
> > diff --git a/security/selinux/Kconfig b/security/selinux/Kconfig
> > index 996d35d950f7..580ac24c7aa1 100644
> > --- a/security/selinux/Kconfig
> > +++ b/security/selinux/Kconfig
> > @@ -42,6 +42,9 @@ config SECURITY_SELINUX_DISABLE
> >         using the selinux=0 boot parameter instead of enabling this
> >         option.
> >
> > +       WARNING: this option is deprecated and will be removed in a future
> > +       kernel release.
> > +
> >         If you are unsure how to answer this question, answer N.
> >
> >   config SECURITY_SELINUX_DEVELOP
> > diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
> > index 278417e67b4c..adbe2dd35202 100644
> > --- a/security/selinux/selinuxfs.c
> > +++ b/security/selinux/selinuxfs.c
> > @@ -281,6 +281,12 @@ static ssize_t sel_write_disable(struct file *file, const char __user *buf,
> >       int new_value;
> >       int enforcing;
> >
> > +     /* NOTE: we are now officially considering runtime disable as
> > +      *       deprecated, and using it will become increasingly painful
> > +      *       (e.g. sleeping/blocking) as we progress through future
> > +      *       kernel releases until eventually it is removed */
> > +     pr_err("SELinux:  Runtime disable is deprecated, use selinux=0 on the kernel cmdline.\n");
>
> Looking for examples of similar deprecations in the kernel, I notice
> that they often use pr_warn_once() or WARN_ONCE() to avoid spamming the
> kernel logs excessively.  They also often include the current process
> name to identify the offending process.  In this case, it probably
> matters little since this is only done (legitimately) by the init
> process and only once, so up to you whether you bother amending it.

Yes, I saw that too and decided we were better off printing something
each time since it really should only ever happen once on a well
behaved system.

> Also for some interfaces, they appear to document the intent to remove
> it in a file under Documentation/ABI/obsolete/ and then later move that
> to removed/ when fully removed.

Thanks, I wasn't aware of that, and couldn't find anything relevant
while grep'ing under Documentation/process.  There used to be a
Documentation/feature-removal.txt (or a file with a similar name)
which tracked these things, but I guess it migrated over to
Documentation/ABI during the last Documentation shuffle a couple of
years ago.

I'll send out an updated patch in just a moment.
diff mbox series

Patch

diff --git a/security/selinux/Kconfig b/security/selinux/Kconfig
index 996d35d950f7..580ac24c7aa1 100644
--- a/security/selinux/Kconfig
+++ b/security/selinux/Kconfig
@@ -42,6 +42,9 @@  config SECURITY_SELINUX_DISABLE
 	  using the selinux=0 boot parameter instead of enabling this
 	  option.
 
+	  WARNING: this option is deprecated and will be removed in a future
+	  kernel release.
+
 	  If you are unsure how to answer this question, answer N.
 
 config SECURITY_SELINUX_DEVELOP
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 278417e67b4c..adbe2dd35202 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -281,6 +281,12 @@  static ssize_t sel_write_disable(struct file *file, const char __user *buf,
 	int new_value;
 	int enforcing;
 
+	/* NOTE: we are now officially considering runtime disable as
+	 *       deprecated, and using it will become increasingly painful
+	 *       (e.g. sleeping/blocking) as we progress through future
+	 *       kernel releases until eventually it is removed */
+	pr_err("SELinux:  Runtime disable is deprecated, use selinux=0 on the kernel cmdline.\n");
+
 	if (count >= PAGE_SIZE)
 		return -ENOMEM;